<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<!--post参数放到请求体中去-->
 <form method="post" action="userServlet">
 用户名:<input type="text" name="username" ><br>
 <input type="submit" value="校验">
 </form>

</body>
</html>